If you're an alchemist, a great way to make extra gold is to do elemental transmutes. For example, on the auction house Eternal Earth might sell for 10 gold and Eternal Air might sell for 40 gold. By transmuting Eternal Earth into Air, you can easily make 30 gold a day for about 10 seconds of work.

In WotLK, the only way to learn these transmutes is by randomly discovering them. Previously this was a time-consuming process that required performing lots and lots of transmutes. However there's a trick to quickly discover all of the transmutes! Here's how:

Have an alchemy skill of 395.

Train "Transmute: Titanium" from your local alchemy trainer.

Get the materials for the Titanium transmute. You'll need 2 Cobalt Bar, 8 Saronite Bar, and 2 Crystallized Life. They cost me about 40 gold on the auction house. If there is no Crystallized Life on the auction house, you can buy an Eternal Life and right-click it to get 10 Crystallized Life.

Get the materials to make lots of elixirs. I grabbed several stacks of Goldclover and lots of Imbued Vials so I could make lots of Elixir of Mighty Fortitude.

Perform the Titanium Transmutation.

Quickly create as many elixirs or potions as you can. I created lots of Elixir of Mighty Fortitude. If the recipe turns green for you, feel free to switch to a higher-level recipe so you get more skill-ups.

You should now have discovered a new transmutation approximately every other potion creation. In the screenshot below, I created 9 elixirs and made 7 new transmutation discoveries. Two of these transmutations are valuable and will make me an easy 30g a day. This has worked for several other people, so go ahead and give it a try. Enjoy!